The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Rolf Gruetter - One of the best experts on this subject based on the ideXlab platform.
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on the origin of the mr image phase contrast an in vivo mr microscopy study of the rat brain at 14 1 t
NeuroImage, 2009Co-Authors: Jose P Marques, Rajika Maddage, Vladimir Mlynarik, Rolf GruetterAbstract:article i nfo Recent studies at high magnetic fields using the phase of gradient-echo MR images have shown the ability to unveil cortical substructure in the human brain. To investigate the contrast mechanisms in phase imaging, this study extends, for the first time, phase imaging to the rodent brain. Using a 14.1 T horizontal bore animal MRI scanner for in vivo micro-imaging, images with an in-plane resolution of 33 μm were acquired. Phase images revealed, often more clearly than the corresponding magnitude images, hippocampal fields, cortical layers (e.g. layer 4), cerebellar layers (molecular and granule cell layers) and small white matter structures present in the striatum and septal nucleus. The contrast of the phase images depended in part on the orientation of anatomical structures relative to the magnetic field, consistent with bulk susceptibility variations between tissues. This was found not only for vessels, but also for white matter structures, such as the anterior commissure, and cortical layers in the cerebellum. Such susceptibility changes could result from variable blood volume. However, when the Deoxyhemoglobin content was reduced by increasing cerebral blood flow (CBF) with a carbogen breathing challenge, contrast between white and gray matter and cortical layers was not affected, suggesting that tissue cerebral blood volume (and therefore Deoxyhemoglobin) is not a major source of the tissue phase contrast. We conclude that phase variations in gradient-echo images are likely due to susceptibility shifts of non- vascular origin.
M. I. Oshtrakh - One of the best experts on this subject based on the ideXlab platform.
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The DFT-DVM theoretical study of the differences of quadrupole splitting and the iron electronic structure for the rough heme models for α- and β-subunits in Deoxyhemoglobin and for deoxymyoglobin
Hyperfine Interactions, 2008Co-Authors: E. I. Yuryeva, M. I. OshtrakhAbstract:Quantum chemical calculations of the iron electron structure and 57Fe quadrupole splitting were made by density functional theory and Xα discrete variation method for the rough heme models for α- and β-subunits in Deoxyhemoglobin and for deoxymyoglobin accounting stereochemical differences of the active sites in native proteins. The calculations revealed differences of quadrupole splitting temperature dependences for three models indicating sensitivity of quadrupole splitting and Fe(II) electronic structure to small variations of iron stereochemistry.
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Ab initio study of the 57Fe quadrupole splitting in the heme models of α- and β-subunits in tetrameric Deoxyhemoglobin
Hyperfine Interactions, 2006Co-Authors: E. I. Yuryeva, M. I. OshtrakhAbstract:Ab initio Xα discrete variation method was used for calculation of quadrupole splitting for the rough heme models in α- and β-subunits of tetrameric Deoxyhemoglobin accounting small stereochemical variations. The differences of theoretical values of quadrupole splitting for these heme models were obtained.
Kamil Ugurbil - One of the best experts on this subject based on the ideXlab platform.
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imaging of brain function using Deoxyhemoglobin and magnetic fields
2012Co-Authors: Kamil UgurbilAbstract:In the two decades since its discovery, functional magnetic resonance imaging (fMRI) has seen a revolution in its ability to image brain function, going from early experiments demonstrating relatively course images of activity in the visual cortex, to mapping cortical columns, and to “brain reading” that constructs mental experiences of an individual, all using the fact that we were endowed with a complex paramagnetic molecule sequestered in our blood vessels and that neuronal activity has spatially-specific metabolic and physiologic consequences. These developments owe their success in part to significant improvements in our understanding of underlying mechanisms operative in functional imaging. These mechanisms and how they come into different data collection schemes are reviewed in this chapter. At the same time, we have seen major advances and refinements in instrumentation, which are also touched upon in this chapter, such as the introduction of ultrahigh field instruments with ever increasing capabilities, novel data acquisition strategies, and new image analysis methods, all of which also dramatically improve data quality. Some of these developments have not yet been incorporated into routine use. If history is a guide, however, the fantastically dynamic nature of the MR methodology, and the very large amount of effort committed to this field of research would predict that in a decade or two, fMRI may be performed using totally different approaches and provide substantially better information than the richness we experience with techniques at the cutting edge today.
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in vitro and in vivo studies of 1h nmr visibility to detect Deoxyhemoglobin and deoxymyoglobin signals in myocardium
Magnetic Resonance in Medicine, 1999Co-Authors: Wei Chen, Yong K Cho, Hellmut Merkle, Yi Zhang, Guangrong Gong, Jianyi Zhang, Kamil UgurbilAbstract:1H nuclear magnetic resonance (NMR) spectroscopy can be used noninvasively to detect the proximal histidyl N delta proton signals of deoxymyoglobin in the myocardium. However, the quantification of deoxymyoglobin is based on the assumption that the deoxymyoglobin signal detected is not contaminated by the Deoxyhemoglobin signals contributed from the blood. The purpose of this study was to conduct in vitro and in vivo 1H NMR studies to examine the in vivo NMR visibility of Deoxyhemoglobin in the myocardium. The results demonstrate that the NMR visibility of alpha and beta subunits of Deoxyhemoglobin is sensitive to the pulse width for spin excitation because of short T2 relaxation times, and they are not NMR visible in the canine myocardium in vivo at 4.7 T when a 0.5-1.0 msec long Gaussian excitation pulse is used. Therefore, the resonance peak detected at approximately 72 ppm (relative to the water resonance) in the ischemic canine myocardium in vivo is dominated by deoxymyoglobin.
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functional brain mapping by blood oxygenation level dependent contrast magnetic resonance imaging a comparison of signal characteristics with a biophysical model
Biophysical Journal, 1993Co-Authors: S Ogawa, Hellmut Merkle, Ravi S Menon, David W Tank, Seonggi Kim, Jutta M Ellermann, Kamil UgurbilAbstract:It recently has been demonstrated that magnetic resonance imaging can be used to map changes in brain hemodynamics produced by human mental operations. One method under development relies on blood oxygenation level-dependent (BOLD) contrast: a change in the signal strength of brain water protons produced by the paramagnetic effects of venous blood Deoxyhemoglobin. Here we discuss the basic quantitative features of the observed BOLD-based signal changes, including the signal amplitude and its magnetic field dependence and dynamic effects such as a pronounced oscillatory pattern that is induced in the signal from primary visual cortex during photic stimulation experiments. The observed features are compared with the results of Monte Carlo simulations of water proton intravoxel phase dispersion produced by local field gradients generated by paramagnetic Deoxyhemoglobin in nearby venous blood vessels. The simulations suggest that the effect of water molecule diffusion is strong for the case of blood capillaries, but, for larger venous blood vessels, water diffusion is not an important determinant of Deoxyhemoglobin-induced signal dephasing. We provide an expression for the apparent in-plane relaxation rate constant (R2*) in terms of the main magnetic field strength, the degree of the oxygenation of the venous blood, the venous blood volume fraction in the tissue, and the size of the blood vessel.
E. I. Yuryeva - One of the best experts on this subject based on the ideXlab platform.
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The DFT-DVM theoretical study of the differences of quadrupole splitting and the iron electronic structure for the rough heme models for α- and β-subunits in Deoxyhemoglobin and for deoxymyoglobin
Hyperfine Interactions, 2008Co-Authors: E. I. Yuryeva, M. I. OshtrakhAbstract:Quantum chemical calculations of the iron electron structure and 57Fe quadrupole splitting were made by density functional theory and Xα discrete variation method for the rough heme models for α- and β-subunits in Deoxyhemoglobin and for deoxymyoglobin accounting stereochemical differences of the active sites in native proteins. The calculations revealed differences of quadrupole splitting temperature dependences for three models indicating sensitivity of quadrupole splitting and Fe(II) electronic structure to small variations of iron stereochemistry.
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Ab initio study of the 57Fe quadrupole splitting in the heme models of α- and β-subunits in tetrameric Deoxyhemoglobin
Hyperfine Interactions, 2006Co-Authors: E. I. Yuryeva, M. I. OshtrakhAbstract:Ab initio Xα discrete variation method was used for calculation of quadrupole splitting for the rough heme models in α- and β-subunits of tetrameric Deoxyhemoglobin accounting small stereochemical variations. The differences of theoretical values of quadrupole splitting for these heme models were obtained.
Jens Frahm - One of the best experts on this subject based on the ideXlab platform.
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simultaneous recording of cerebral blood oxygenation changes during human brain activation by magnetic resonance imaging and near infrared spectroscopy
Journal of Cerebral Blood Flow and Metabolism, 1996Co-Authors: Andreas Kleinschmidt, Hellmuth Obrig, Martin Requardt, Klausdietmar Merboldt, Ulrich Dirnagl, Arno Villringer, Jens FrahmAbstract:Changes in cerebral blood oxygenation due to functional activation of the primary sensorimotor cortex during a unilateral finger opposition task were simultaneously mapped by Deoxyhemoglobin-sensitive magnetic resonance imaging (MRI) and monitored by near-infrared spectroscopy (NIRS). Activation foci along the contralateral central sulcus displayed task-associated increases in MRI signal intensity, indicating a concomitant decrease of the focal concentration of Deoxyhemoglobin. This interpretation was confirmed by simultaneous reductions in Deoxyhemoglobin measured optically. Since observation of the latter effect required exact spatial matching of the MRI-detected activation foci and position of the fiber optic bundles (“optodes”) used for transmitting and receiving light, it may be concluded that optical recordings of changes in Deoxyhemoglobin during functional challenge probe only a restricted brain tissue region. While Deoxyhemoglobin responses seen by NIRS were smaller for ipsi- than for contralater...
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functional mri of human brain activation at high spatial resolution
Magnetic Resonance in Medicine, 1993Co-Authors: Jens Frahm, Klausdietmar Merboldt, W HanickeAbstract:Functional activation maps of the human visual cortex were obtained at a spatial resolution almost two orders of magnitude better than achievable by positron emission tomography and within measuring times of a few seconds. Transient alterations in the concentration of paramagnetic Deoxyhemoglobin were conveniently detected at 2.0-T with use of RF-spoiled FLASH MRI sequences employing gradient echo times of 6 to 60 ms and voxel sizes of 2.5 to 39 μl.